[128729] in cryptography@c2.net mail archive
Re: Looking through a modulo operation
daemon@ATHENA.MIT.EDU (lists@notatla.org.uk)
Wed Jul 23 09:29:56 2008
Date: Wed, 23 Jul 2008 03:46:47 +0100
To: matt.ball@ieee.org, cryptography@metzdowd.com
In-Reply-To: <ed843b100807201514r3a985135tfa4e691750838b3e@mail.gmail.com>
From: lists@notatla.org.uk
"Matt Ball" <matt.ball ieee.org> wrote
> Here is a C implementation of __random32:
>
> typedef unsigned long u32;
> struct rnd_state { u32 s1, s2, s3; };
> static u32 __random32(struct rnd_state *state)
> {
> #define TAUSWORTHE(s,a,b,c,d) ((s&c)<<d) ^ (((s <<a) ^ s)>>b)
>
> state->s1 = TAUSWORTHE(state->s1, 13, 19, 4294967294UL, 12);
> state->s2 = TAUSWORTHE(state->s2, 2, 25, 4294967288UL, 4);
> state->s3 = TAUSWORTHE(state->s3, 3, 11, 4294967280UL, 17);
>
> return (state->s1 ^ state->s2 ^ state->s3);
> }
I see TAUSWORTHE (briefly tested with the above constants) isn't a
permutation of the 32-bit input state and is going to get very dull
when s is 0.
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